66 FERROUS SULPHATE with ammonia : in presence of chlorine, the paper turns blue and in presence of hydrochloric acid white fumes form round the rod. 3. Ferrous Chloride. — The i : 100 solution is tested with a few drops of freshly prepared dilute potassium ferricyanide solution : in presence of ferrous salts a blue coloration is formed. 4. Arsenic. — To I c.c. of the i : i solution, 5 c.c. of Bettendorf's re- agent are added : no brown coloration should be formed within an hour. 5. Nitrates and Extraneous Metals. — i gram, dissolved in 20 c.c. of water, is treated with excess of ammonia and filtered. 2 c.c. of the filtrate are boiled until the ammonia is completely expelled and is then mixed with cone, sulphuric acid, ferrous sulphate solution being poured carefully on to the surface of the liquid : any brown, ring at the zone of contact of the two layers is observed (nitric acid). The remainder of the filtrate is evaporated to dryness and calcined to ascertain if appreciable residue remains (extraneous metals). FERROUS ACETATE Industrial use is made of crude ferrous acetate (pyrolignile of iron) solution, which is a greenish-black liquid of marked einpyreumatic odour. This solution is usually of 12-15° Baiime, but stronger ones of 20-30° Baum<$ are also prepared, these containing more tarry matters which arc precipitated on dilution. 1. Grade. — Determined with an ordinary Baurne hydrometer. 2. Behaviour on Dilution.— i vol. is diluted with 250 vols. of water and the colour of the liquid and any precipitation of tarry substuuc.es noted, 3. Ferric Salts. — The sample is diluted i : 10, acidified with hydro- chloric acid and tested with potassium ferrocyanide. 4. Sulphates, Chlorides,—- The. i : 10 solution of the. sample is acidified with nitric acicl and tested with barium chloride and with silver nitrate. An appreciable proportion of sulphate is determined us barium sulphate, while hydrochloric acid may be estimated as silver salt. 5. Determination of the Acetic Acid.-— This is done as in calcium acetate (q.v.). 6. Determination of the Iron.—- 1-2 grams are evaporated to dryness and the residue cautiously ignited and dissolved in hydrochloric acid, the iron being determined in the solution by precipitation with ammonia. Pyrolignitc of iron solution or mordant for black (not to bo confused with the basic sulphate), when diluted with water (test 2), .should give a fine blue colora- tion, which slowly changes to greenish and becomes opaque ; it should not con- tain any large proportions of ferric salts or sulphates. FERROUS SULPHATE FeSO, + 7HaO - 278 : Forms large or small, pale green crystals or crystalline powder ; in the air it effloresces somewhat, and it dissolves in 1-5 parts of water and is insoluble in alcohol. It often exhibits yellowish spots of ferric oxide orpanto with a little water and poured into 200 o.c.